In the sphere of fuel delivery for motor vehicles, the tanks of a storage facility of a service station are conventionally filled with different fuel types. In particular, one distinguishes the fuels referred to as light fuels, such as 98-octane unleaded gasoline, commonly referred to as “98 gasoline”, 95-octane unleaded gasoline, commonly referred to as “95 gasoline”, the mixture of gasoline and ethanol commonly referred to as “biofuel”, or analogous, and the fuels referred to as heavy fuels, such as fuel oil or diesel fuel. The main difference between these two fuel types lies in the markedly higher volatility of the light fuels in relation to the heavy fuels at ambient temperatures, notably between −30° C. and +50° C.
For the light fuels, vapours with high fuel contents are given off from the tanks as they are filled. In order to limit as much as possible atmospheric pollution during filling of the tanks, the vent gases with high fuel vapour contents are not released to nature, but they are generally collected and sent from the light fuel tanks to the tank of the delivery truck. Furthermore, in order to limit the fuel losses undergone by the service station operator, notably in form of fuel vapours made up of volatile organic compounds, document WO-A-03/006,358 proposes using a condenser on each vent pipe connected to a light fuel tank. These condensers significantly reduce the fuel content of the vent gases sent to the tank of the delivery truck, thanks to cooling of the vent gases from the light fuel tanks. The condensates obtained are redirected to the corresponding tank by gravity.
Although such a facility reduces the losses undergone by the service station operator, the fuel losses are not totally eliminated. The volatile gases recovered in the tank of the delivery truck are expelled only when the truck is subsequently filled with fuel and sometimes the truck driver even carries out illegal degassing to the atmosphere so as to avoid transportation of gases considered to be dangerous.
Besides, upon light fuel distribution from tanks, exterior gas is generally sucked in to compensate for the fuel outflow and to maintain a pressure balance in the tank. The light fuel dispensing nozzles of some service stations are thus equipped with suction ports for sucking the fuel vapours released upon filling of the tank of a motor vehicle and the gases thus sucked are sent out of the light fuel tanks when the driver fills up. A collector connected to all the vent pipes of the light fuel tanks enables, if necessary, to pass the sucked gas from the tank into which it is allowed to the tank from which the fuel is distributed, so as to balance the pressure in all the light fuel tanks. Now, the proportion of sucked gas is generally higher, by about 15%, than the volume of fuel delivered for light fuels. Current facilities are therefore provided, in the vent pipes associated with the light fuel tanks, with safety valves set at +30 mbar and −15 mbar. Volatile organic compounds can thus be discharged to the atmosphere at the level of these valves in case of overpressure.
In existing facilities, there is no suction of the aforementioned type for heavy fuel tanks. Besides, the current regulations require separate collectors (two independent collectors or a collection unit subdivided into two sealed parts by a tight wall) for, respectively, the light fuels and the heavy fuels. Only the collector or the part of the collection unit associated with the light fuels is provided with means for connection to the tank of the delivery truck during filling of the tanks so as to prevent the formation of explosive gas mixtures.
Currently, for a conventional service station with a yearly distribution of typically 17 million litres light fuel, about 2%, i.e. 34,000 litres, are vaporized, i.e. lost for the operator and transported by the delivery truck prior to being degassed, at best, at the refinery when filling the truck again.
The goal of the invention is to overcome these drawbacks and, more particularly, to reduce fuel losses for the operator of a service station without requiring bringing expensive adjustments to existing facilities, while best limiting atmospheric pollution.